Align loopcuts (so it looks like one big face)
A series of narrow/thin faces like this will easily lead to such problem if the "big face" isn't as flat as they were coplanar. So the main problem here is about topology actually.

Try following steps to solve this issue:


Select all narraow/thin faces that form the "big face", then press F (or X > Dissolve Faces) to make it as a big Ngon face;
Press Spacebar and search for Split Non-Planar Faces (or access from Mesh > Clean up > Split Non-Planar Faces); F6 to adjust the max split angle until you get the expected result. (In your particular case, setting to 0° will triangulate it too, which means you can ignore step 3 below);
CtrlT to split Ngon faces into triangles. (optional)




Tip: For Step 2, You can also split it manually instead. Two nice ways are:


Press K to enable Knife tool, then cut line(s) on the big face;
Select two vertices, then J to connect them by adding a new edge on that face.


Either way above can help when doing retopology.



If you really don't want to change the topology too much, then a quick and dirty way at least would be: